The global positioning system, or GPS, that people use every day for navigation, may actually provide an easy avenue for a terrorist attack. GPS jamming is becoming an increasing problem; GPS expert and assistant professor at the University of Texas recently exposed how location technology creates a gaping hole in national security. With nothing more than a small antenna, a laptop, $3,000 device known as a GPS “spoofer” and some basic hacking knowledge, Todd Humphreys commandeered a 210-foot luxury yacht in the Mediterranean Sea, showing how any hacker could exploit a GPS system to take control of a vehicle.

Humphreys’ team built the world’s most powerful GPS spoofer, which dupes GPS antennas with fake signals. In a demonstration with Fox News, Humphreys showed how his device injected spoofing signals into the ship’s GPS antennas, providing inaccurate information. A hacker could use this to hijack the ship and disorient it without alerting the crew.

“Imagine shutting down a port,” Humphrey’s said. “Imagine running a ship aground. These are the kinds of implications we’re worried about.”

The attacks aren’t limited to ships. Spoofing attacks can be used to attack any system using GPS technology, including commercial airlines and drones. Congress has had Humphrey’s speak with the FAA, CIA and Pentagon on GPS security, but little has been done to address the threat.

GPS is shut down every day for 10 minutes around the London Stock Exchange, most likely by a delivery driver using a cheap (less than $80) jamming device to dodge his bosses’ attempts to track his location, according to the Economist. These devices use electromagnetic noise to block GPS signals but also affect other GPS antennas near them. They are illegal in the U.S., and, although they are legal to purchase in the UK, it is illegal to use them.

North Korea uses them to block GPS signals in South Korea. In 2012, North Korea ran them for 16 days, disrupting GPS on 1,016 aircraft and 254 maritime ships.

Humphreys' experiment was the first time that showed how a hacker could actually control a vehicle through GPS, not just interfere with it.

Some governments are experimenting with new, more secure location tracking systems, but GPS is so ubiquitous that it has become indispensable for many people. For now, they remain vulnerable.

“People need to know this kind of thing is possible with a relatively small budget, and they can with a very simple system steer the ship off-course without the captain knowing,” Humphreys said.